Download Down Syndrome information sheet

Regional Autism Team
Factsheet: Down syndrome (DS)
Origins
Other names
Prevalence
English physician John Langdon Down first characterized Down syndrome (DS) as
a separate form of disability in 1862. In 1959, Jérôme Lejeune reported the
discovery that Down syndrome resulted from an extra chromosome. However this
claim has been disputed, and in 2014 the Scientific Council of the French Federation
of Human Genetics unanimously awarded its Grand Prize to his colleague Marthe
Gautier for this discovery. As a result of this discovery, the condition became known
as Trisomy 21.
Trisomy 21
DS is the most common chromosomal cause of intellectual disability occurring in
approximately 1/600 births in Ireland. (Globally, as of 2010, Down syndrome
occurs in about 1 per 1000 births)
Autism Spectrum Disorder (ASD) is reported in 7-15% of DS cases, which is 10-25%
higher than the general population (DiGuiseppi et al. 2010). ASD is more prevalent
in individuals with Down Syndrome who are more cognitively impaired. Higher
rates of impaired social skills have been reported in family members of individuals
with DS and ASD in comparison to individuals with DS without ASD (Lowenthal et
al, 2007).
Features
Although the majority of children with DS do not have a coexisting psychiatric
condition, it is estimated that 20-38% have psychiatric co-morbidity and
symptomatolgy including attention problem, conduct disorder, social withdrawal,
psychotic behaviours as well as ASD.
Social interaction & Behaviours
People with DS are generally known for their cheerful and friendly demeanours
without significant impairment in social interactions. Estimated that rates of
disruptive behaviours are between 15-7%.
Physical Features:
Small chin, slanted eyes, poor muscle tone, a flat nasal bridge, a single crease of
the palm, and a protruding tongue, a flat and wide face, a short neck, excessive
joint flexibility, extra space between big toe and second toe, abnormal patterns on
the fingertips and short fingers. Instability of the atlanto-axial joint occurs in
approximately 20%.Hip dislocations may occur without trauma in up to a third of
people with DS.
Growth in height is slower resulting in adults who tend to have short stature—the
average height for men is 154 cm (5 feet 1 inch) and for women is 142 cm (4 feet
8 inches). Individuals with DS are at increased risk for obesity as they age. There
are growth charts specifically for children with DS.
Neurological features:
A level of intellectual disability. Those with mosaic DS typically have IQ scores
10–30 points higher. Many developmental milestones are delayed with the ability
to crawl typically occurring around 8 months rather than 5 month and the ability
to walk independently typically occurring around 21 months rather than
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14 months. Commonly individuals with DS have better language understanding
than ability to speak. Children and adults with DS are at increased risk of epileptic
seizures which occur in 5–10% of children and up to 50% of adults. This includes
an increased risk of a specific type of seizure called infantile spasms. Many (15%)
who live 40 years or longer develop dementia of the Alzheimer's type. In those who
reach 60 years of age, 50–70% have the disease.
Senses
Vision problems occur in 38 to 80%. Between 20 and 50% have strabismus.
Cataracts occur in 15%, and may be present at birth. Keratoconus (thin, coneshaped corneas) and glaucoma (increased eye pressure) are also more common, as
are refractive errors requiring glasses or contacts. Brushfield spots (small white or
grayish/brown spots on the outer part of the iris) are present in 38 to 85% of
individuals.
Hearing problems are found in 50–90% of children with DS. This is often the
result of otitis media with effusion which occurs in 50–70% and chronic ear
infections which occurs in 40 to 60%. Ear infections often begin in the first year of
life and are partly due to poor Eustachian tube function. Excessive ear wax can also
cause hearing loss due to obstruction of the outer ear canal.
Heart
The rate of congenital heart disease in newborns with DS is around 40%. Of those
with heart disease about 80% have an atrioventricular septal defect or ventricular
septal defect. Mitral valve problems become common as people age, even in those
without heart problems at birth. Other problems that may occur include: tetralogy
of Fallot and patent ductus arteriosus.
Causes
Endocrine
Problems of the thyroid gland occur in 20–50% of individuals with DS. Low
thyroid is the most common form, occurring in almost half of all individuals.
DS is caused by having three copies of the genes on chromosome 21, rather than
the usual two. Those who have one child with DS have about a 1% risk of having a
second child with the syndrome. It can be a full or partial trisomy of chromosome
21, although occasionally an unbalanced translocation involving chromosome 21
has been identified. DS is caused by a failure of the 21st chromosome to separate
during egg or sperm development. As a result, a sperm or egg cell is produced with
an extra copy of chromosome 21; this cell thus has 24 chromosomes. When
combined with a normal cell from the other parent, the embryo and baby has 47
chromosomes, with three copies of chromosome 21. About 88% of cases of trisomy
21 result from non separation of the chromosomes in the mother, 8% from nonseparation in the father, and 3% after the egg and sperm have merged.
There are 3 main types:
1.
The most common cause (approximately 92–95% of cases) is a complete
extra copy of chromosome 21, resulting in trisomy 21.
2.
In 1 to 2.5% of cases, some of the cells in the body are normal and others
have trisomy 21, known as mosaic Down syndrome.
3.
Robertsonian translocation, isochromosome, or ring chromosome: These
contain additional material from chromosome 21 and occur in approximately 2.5%
of cases. Some children without DS may inherit the translocation and have a
higher risk of having children of their own with DS In this case it is sometimes
known as familial DS
Regional Autism Team. Differential Diagnosis information. April 2014.
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Diagnosis of
DS
Possible shared
features
between DS &
ASD
Differential
Features with
ASD
When screening tests predict a high risk of DS, a more invasive diagnostic test
(amniocentesis or chorionic villus sampling) is needed to confirm the diagnosis.
Amniocentesis and chorionic villus sampling are more reliable; however, they
carry an increased risk of miscarriage of between 0.5 and 1%.There is also an
increased risk of limb problems in the offspring due to the procedure.
Abortion rates
About 92% of pregnancies in the United Kingdom and Europe with a diagnosis of
DS are terminated.
After birth
The diagnosis can often be suspected based on the child's physical appearance at
birth. An analysis of the child's chromosomes is needed to confirm the diagnosis
and determine if a translocation is present as this may help determine the risk of
the child's parents having further children with DS.

Typically delays in social and communication in line with cognitive profile.

High level of stereotypic movements in DS.

Children with DS may lack spontaneous seeking to share enjoyment, interest
or achievement with other people, but generally more pronounced in children with
ASD

Children with DS may have reduced social or emotional reciprocity

Difficultly initiating and sustaining conversations

Immediate and delayed echolalia
Social Interaction & communication:
From Cohen et. al (2009) research to following features differentiated DS + ASD
from DS alone:*isolates self from others (most significant)
DS alone tend to have:

Appropriate eye contact, facial expression, use of body language and use of
gestures.

Tend to communicate for a variety of reasons and can generalise
communication across settings

May watch peers, parallel play, develop peer relationship at developmental
level

Children with DS generally develop some communication system/will
compensate for lack of verbal language with alternative modes of communication
Play
DS tend to present with creative play at developmental level.
Stereotypical behaviours & Repetitive routines:
From Cohen et. Al (2009) research to following features differentiated DS + ASD
from DS alone: Presence of odd, bizarre behaviour, Stereotyped repetitive
movements. Moves or rolls head back and forth
DS tend not to have need for routine or rituals or preoccupation in parts of objects.
Emotions/behaviour: From Cohen et. al (2009) research to following features
differentiated DS + ASD from DS alone: High levels of anxiety or fear
Recommendati
ons for
Diagnosis of coexisting ASD can be challenging due to difficulty differentiating
autistic-type behaviours from stereotypical behaviours and communications and
Regional Autism Team. Differential Diagnosis information. April 2014.
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diagnostic
assessment
other cognitive impairments associated with ID.

Individuals with DS are at increased risk for sensory conditions (hearing
loss) and motor difficulties (hypotonisa) which may affect timing and fluidity of
social and communicative behaviours. Efforts to correct sensory deficits before
screening for an ASD may be appropriate

MCHAT and SCQ have been found to be highly sensitive in identifying
children with DS and ASD. (DiGuiseppi et al, 2010)

important to conduct a detailed and fine grained assessment of ASD
Please note: reported agreement of ADI-R and ADOS is lower that reported by
authors in individual with ID. Ability of the ADI-R to discriminate ASD and Severe
ID is somewhat limited (Bildt et al, 2004, Cray 2008)
More
information
and useful
reading
Carter et al (2009). Autistic Spectrum Disorders in Down Syndrome: Further
delineation and distinction for other behavioural abnormalities. American Journal
of Medical Genetics Part B, 144B:87-94.
*DiGuiseppi et al, (2010). Screening for Autism Spectrum Disorder in Children
with Down Syndrome: Population prevalence and Screening Test Characterises.
Journal of Developmental Behavioural Paediatrics, vol. 31p 181-191.
*Moss, J., P. Howlin and C. Oliver. (2011) The assessment and presentation of
Autism Spectrum Disorders and associated characteristic in individuals with
severe intellectual disability and genetic syndromes. The Oxford Handbook of
Intellectual Disability and Development.
Reilly, C. (2009). Autism Spectrum Disorders in Down syndrome: A review.
Research in Autism Spectrum Disorders. Vol 3. p. 829-839.
Down Syndrome Ireland: http://downsyndrome.ie/
* Available in RAST dropbox
.
Regional Autism Team. Differential Diagnosis information. April 2014.
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